Several extracorporeal renal replacement procedures, such as dialysis, hemodialysis, hemofiltration, hemodiafiltration, ultrafiltration, and plasmapheresis are used to provide replacement or supplementation of a patient's natural renal function in order to remove fluid and/or waste products from their blood. The specific procedure is tailored to the specific needs of the particular patient. For example, dialysis is used to remove soluble waste and solvent from blood. Hemofiltration is used to remove plasma water and dissolved waste from blood while replacing the removed volume with replacement solution. Hemodiafiltration is used to remove both unwanted solute (soluble waste) and plasma water from blood. Ultrafiltration is a species of hemofiltration where only volume and dissolved components are released; and plasmapheresis is used to remove blood plasma by means of a plasmapheresis filter.
For certain patients, renal replacement procedures may extend over hours, days, months and even years. In general, current systems for monitoring and controlling renal replacement procedures lack the flexibility and accuracy required to perform such procedures on neonates. This is mainly due to the absence of a satisfactory automatic control of the pumps employed. Because of the patient risk involved in using such equipment, health care personnel may measure the fluid removed from the patient on an hourly basis. The continuing need to monitor the fluid removed and patient responses lead to a significant increase in nursing care and, thus, increases the cost of the therapy. Therefore, there is a need to improve the level of autonomy for the systems such that the procedure is less time consuming for medical personnel, and consequently less costly. However, the enhanced autonomy must not come at the expense of patient safety.
Due to the time-varying nature of renal function replacement and supplementation systems, the dynamics of fluid pumping may change over time. For example, the characteristics of system components such as tubing, filter, and connectors may vary slowly over time due to protein deposit or as occlusion of the path for fluid flow. As the membrane changes, the pumping rate of the pump must be altered to compensate for the altered filter to maintain the same function. Current systems for monitoring and controlling renal replacement procedures lack the ability to autonomously correct these time-dependent flow rate variations with high accuracy, rapid response, and minimal overshoot or transient variations following correction. In one sense, most conventional systems, at best, tend to be reactive, rather than proactive, during a procedure.
A particular need for the ability to control fluid pumping arises in patients undergoing hemodialysis. During a hemodialysis procedure, dissolved materials are removed from the blood and added to the blood down their respective concentration gradients. In addition, plasma water and dissolved content are removed through a porous membrane down a pressure gradient in a process known as ultrafiltration. The clinical problem observed during hemodialysis is that, during the intrinsic dual treatment processes, replacement of renal function reduces the patient's intravascular or blood volume. This impacts the heart's ability to pump blood to the tissues and causes many unwanted side effects including, but not limited to, cramping, nausea, vomiting, and diaphoresis. Such cardiac function compromises can also challenge blood flow to the heart itself and cause arrhythmia or even a heart attack.
Conventional solutions to these adverse side effects is to buffer the intravascular volume reduction with effecting a change in the osmotic fluid shift. While some patients may respond, the effects are not very often consistent and, in particular, patients with intradialytic hypotension (IDH) continue to have problems. The consequences of IDH may include pain, loss of functional days and death.
Another conventional approach is to monitor the patient's hematocrit on line and use the hematocrit measurements to monitor the blood volume. The deficiency of this conventional approach is that, if one makes an adjustment based on the hematocrit, the system changes as the fluid removal rate also alters the cardiovascular physiology. Consequently, the target for alleviating the heart's inability to pump blood to the tissues will continuously shift without control. Merely reducing the fluid removal rate may paradoxially induce a state that could worsen the hypotension by interfering with the bodies physiologic response.
Therefore, there is a need for an improved hemodialysis system that can overcome these and other deficiencies of conventional hemodialysis systems.